- Latin synonym: Listera ovata
- Name also: Common Twayblade, European Common Twayblade
- Family: Orchid Family – Orchidaceae
- Growing form: Perennial herb. Rootstock horizontal. Forms stands.
- Height: 20–60 cm (8–25 in.). Stem branchless, with glandular hairs.
- Flower: Perianth irregular (zygomorphic), lime greenish–brownish, approx. 1–2 cm (0.4–0.8 in.) wide. Tepals 6, in 2 whorls, curving towards each other, one elaborated into labellum. Labellum under perianth, spurless, lime green, tip deeply 2-lobed. Androecium and gynoecium fused into a column, stamens 1, stigmas 2. Inflorescence a many-flowered, quite lax spike.
- Leaves: Two opposite leaves on lower half of stem, stalkless, amplexicaul. Blade widely elliptic, parallel-veined, with entire margin.
- Fruit: Egg-shaped, erect capsule. Seeds tiny, like dust.
- Habitat: Broad-leaved forests, coppices, rich mixed swamps and bogs.
- Flowering time: June–July.
- Endangerment: Protected in all of Finland except the Åland Islands.
Not all orchids are colourful and showy. (Common) twayblade’s small green flowers hide behind the surrounding summer foliage so well that even pollinators are only able to find it by its sharp, sweetish fragrance, which is somewhat reminiscent of cow parsely. Once the inflorescence has been located, insects climb the hairy stem towards it, and a downward-curving lip acts as a bridge to the flower. The upper tepals provide protection, stopping the nectar being enjoyed from the wrong direction. The nectar flows along the lip’s narrow groove, and the sucking insect will at some point make contact with the tip of the column – the pollinia then suddenly brushes against the insect’s forehead. It might be assumed that this would give the pollinator quite a scare, but usually they are quite calm about it and continue pollinating the plant. Twayblade’s flowers are visited by all kinds of insects, perhaps more than any other orchid, but the best pollinators are ichneumonoid flies, symphytans and triungulids. Twayblade specializes in being pollinated by these insects, so it has no reason to try to attract bees and flower flies – rather it is more interested in hiding from them as they are unable to pollinate the plant.
Although twayblade’s flowers are completely green, its size makes it easier to find than it’s smaller relative lesser twayblade (N. cordata). Twayblade propagates itself with its creeping rootstock and can form broad, mat-like stands. It is only abundant on the Åland Islands; on mainland Finland it is rare, usually few and far between, and it is often very delicate.